Acceleration sensors are used in a wide range of fields, including, for example, car crash safety testing, robots, transportation equipment, equipment relating to nuclear power generation, and space and aeronautical equipment and the like. In particular, unlike the alternating current type that only detects the amount of change in acceleration, acceleration sensors used in seismographs, car suspensions, measurement of aseismatic characteristics of building structures and inertial navigation systems and the like are of the so-called direct current type that detects the acceleration of a set value (hereafter called “direct current acceleration sensor”).
In such direct current acceleration sensors, conventionally the acceleration sensor that is the standard measurement object is a piezoelectric type acceleration sensor. However, piezoelectric type acceleration sensors are acceleration sensors (hereafter called “alternating current acceleration sensors”) that can only detect alternating current acceleration; as yet, no calibration apparatus has been developed that calibrates using shock acceleration an acceleration sensor, as used in a seismograph or the like, that detects acceleration from direct current acceleration.
Conventionally, a technique of installing an acceleration sensor on a single axis vibration table and using a laser interferometer to measure the motion of the vibration table has been regarded as having the highest reliability and has been used as the primary standard. As a technique for generating shock acceleration, there has been proposed a technique in which a metal projectile is launched from a simple tube to impact the end of a rod, generating an elastic wave pulse in the rod, and an acceleration sensor attached to the other end surface of the rod is used to evaluate the frequency characteristics using the shock acceleration generated when the pulse reflects at the other end surface of the rod.
The above technique of impacting a projectile against the end of a rod has a drawback in that, since the duration time of the elastic wave generated in the rod cannot be controlled, the duration time of the generated shock acceleration is too short and there is too much spread in the frequency band.
Also, because a direct current acceleration sensor is subject to the effect of gravity, it has been impossible to clarify the effect that the acceleration applied as a direct current component has on the frequency characteristics. That is, although it is necessary to examine the effect that installation location and ground slope have on the characteristics of a direct current acceleration sensor on which gravity acceleration is applied as the direct current component, such as that used in a seismograph, there has been no technology that satisfies that necessity.
Moreover, when calibrating a direct current accelerometer, the direct current accelerometer can be attached to a vibration table and low shock acceleration generated by the vibration table, but even if low shock acceleration is generated in a vertical direction, it is very difficult to suppress acceleration generated in a horizontal direction.
Also, the above technique of impacting a projectile against a metal rod merely generates an elastic wave pulse in the metal rod, so it has not been possible to control the frequency band of the generated shock acceleration.
In view of the above, an object of the present invention is to provide a method of measuring the frequency characteristics of a direct current acceleration sensor that enables the shock acceleration waveform and frequency band to be freely controlled and readily enables accurate measurement and evaluation including evaluation of the effect that gravity acceleration has on the frequency characteristics of a direct current acceleration sensor that detects direct current acceleration, and an apparatus that implements the method.
Another object of the present invention is to provide a method of calibrating an acceleration sensor by generating shock acceleration in which the duration time, peak value, waveform, waveform spectrum and the like of the acceleration waveform applied to the acceleration sensor that is to be calibrated are readily controlled, and a calibration apparatus.
The present invention is intended to resolve the above problems in accordance with the basic concept described below. That is, the center axis of a metal rod that propagates an elastic wave pulse is disposed in the direction of gravity acceleration. Acceleration is generated in the process of the reflection of the elastic wave pulse that propagates in the metal rod at the end surface.
In order to prevent the distortion of the elastic wave pulse, the metal rod holding function is disabled for the very short time (10 ms or below) that is called the pulse reflection time. Even if the holding is disabled for a short time, owing to the inertia of the rod, the distance it falls can be almost ignored.
A data acquisition method and signal processing is used to deal with dynamic characteristics (gain characteristics, phase characteristics) of the direct current acceleration sensor at a specific frequency.
The effect that differences in the direction of gravity acceleration have on the frequency characteristics of the direct current acceleration sensor can be found by inclining a metal rod that propagates the elastic wave pulse and a projectile launch tube disposed along the same axis.
The effect that an inclination of the table to which the direct current acceleration sensor is attached has on the frequency characteristics of the direct current acceleration sensor can be found by comparing the frequency characteristics when the metal rod is inclined with the frequency characteristics when it is not inclined.
Furthermore, multiple projectile launch tubes are used to control the frequency band of the elastic wave produced in the metal rod. As it is an elastic wave so the principle of superposition applies, it is possible to control the frequency band of the generated acceleration by controlling the projectile launch timing and by controlling the elastic wave pulse duration time.
The above-described basic concept can be implemented by employing the specific method and apparatus of the present invention described below.
The present invention provides a method for measuring frequency characteristics of a direct current acceleration sensor comprising supporting a metal rod with a center axis thereof aligned with a direction of gravity acceleration, impacting one of end surfaces of the metal rod with a projectile to generate and propagate an elastic wave pulse in the metal rod, using a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, using a strain gauge provided on a side surface of the metal rod to measure metal rod strain caused by the impact of the projectile against the other end surface of the metal rod, and obtaining a frequency response of the direct current acceleration sensor from a signal from the direct current acceleration sensor and a signal from the strain gauge.
The present invention also provides a method for measuring frequency characteristics of a direct current acceleration sensor comprising supporting a metal rod with a center axis thereof aligned with a direction of gravity acceleration, impacting one of end surfaces of the metal rod with a projectile to generate and propagate an elastic wave pulse in the metal rod, using a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, using an optical measuring instrument to measure a velocity of motion of the other end surface of the metal rod arising when the elastic wave pulse reflects at the other end surface of the metal rod, and obtaining a frequency response of the direct current acceleration sensor from a signal from the direct current acceleration sensor and a signal from the optical measuring instrument.
The present invention also provides a method for measuring frequency characteristics of a direct current acceleration sensor comprising supporting a metal rod with a center axis thereof inclined at a prescribed angle to a direction of gravity acceleration, impacting one of end surfaces of the metal rod with a projectile to generate and propagate an elastic wave pulse in the metal rod, using a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, using a strain gauge provided on a side surface of the metal rod to measure metal rod strain caused by the impact of the projectile against the other end surface of the metal rod, and obtaining from a signal from the direct current acceleration sensor and a signal from the strain gauge a frequency response of the direct current acceleration sensor, with the direct current acceleration sensor affected by the gravity acceleration, and comparing data of the frequency response with data of the frequency response of the direct current acceleration sensor obtained by the first mentioned method, thereby obtaining characteristics with respect to the gravity acceleration in the frequency response of the direct current acceleration sensor.
The present invention also provides a method for measuring frequency characteristics of a direct current acceleration sensor comprising supporting a metal rod with a center axis thereof inclined at a prescribed angle to a direction of gravity acceleration, impacting one of end surfaces of the metal rod with a projectile to generate and propagate an elastic wave pulse in the metal rod, using a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, using an optical measuring instrument to measure a velocity of motion of the other end surface of the metal rod arising when the elastic wave pulse reflects at the other end surface of the metal rod, and obtaining from a signal from the direct current acceleration sensor and a signal from the optical measuring instrument a frequency response of the direct current acceleration sensor in a state in which the gravity acceleration affects the direct current acceleration sensor and comparing data of the frequency response with data of the frequency response of the direct current acceleration sensor obtained by the second mentioned method, thereby obtaining characteristics with respect to gravity acceleration in the frequency response of the direct current acceleration sensor.
The present invention also provides a method for measuring frequency characteristics of a direct current acceleration sensor comprising supporting a metal rod with a center axis thereof aligned with a direction of gravity acceleration, releasing support of the metal rod to produce a free fall state, during a period of releasing the support of the metal rod, impacting one of end surfaces of the metal rod with a projectile to generate and propagate an elastic wave pulse in the metal rod, using a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, using a strain gauge provided on a side surface of the metal rod to measure metal rod strain caused by the impact of the projectile against one of the end surfaces of the metal rod, supporting the metal rod immediately after measuring the strain, and obtaining a frequency response of the direct current acceleration sensor from a signal from the direct current acceleration sensor and a signal from the strain gauge.
The present invention also provides a method for measuring frequency characteristics of a direct current acceleration sensor comprising supporting a metal rod with a center axis thereof aligned with a direction of gravity acceleration, releasing support of the metal rod to produce a free fall state, during a period of releasing the support of the metal rod, impacting one of end surfaces of the metal rod with a projectile to generate and propagate an elastic wave pulse in the metal rod, using a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, using an optical measuring instrument to measure a velocity of motion of the other end surface of the metal rod arising when the elastic wave pulse reflects at the other end surface of the metal rod, supporting the metal rod immediately after measuring the velocity of motion, and obtaining a frequency response of the direct current acceleration sensor from a signal from the direct current acceleration sensor and a signal from the optical measuring instrument.
Any one of the first, third and fifth mentioned methods for measuring the frequency characteristics of the direct current acceleration sensor, in which the one end surface of the metal rod is impacted with the projectile to generate the elastic wave pulse in the metal rod, further comprises taking as an input signal to the direct current acceleration sensor provided on the other end surface of the metal rod dynamic displacement, velocity or acceleration in a direction normal to the other end surface produced when the elastic wave pulse generated by the impact of the projectile reflects at the other end surface, using the direct current acceleration sensor to detect, and the strain gauge provided on the side surface of the metal rod to measure, the input signal as a function of time, carrying out signal processing with respect to an output signal from the direct current acceleration sensor and an output signal from the strain gauge, and using data that has been signal processed as a basis for measuring gain-frequency characteristics, phase-frequency characteristics and peak sensitivity of the direct current acceleration sensor in respect of each of dynamic displacement detection function, velocity detection function and acceleration detection function of the direct current acceleration sensor.
Any of the first, third and fifth mentioned methods for measuring the frequency characteristics of the direct current acceleration sensor, in which the one end surface of the metal rod is impacted with the projectile to generate the elastic wave pulse in the metal rod, further comprises taking as an input signal to the direct current acceleration sensor provided on the other end surface of the metal rod dynamic displacement, velocity or acceleration in a direction normal to the other end surface produced when the elastic wave pulse generated by the impact of the projectile reflects at the other end surface, using the direct current acceleration sensor to detect, and the strain gauge provided on the side surface of the metal rod to measure, the input signal as a function of time, carrying out signal processing of an output signal from the direct current acceleration sensor and an output signal from the strain gauge, carrying out error correction of the output signal from the strain gauge based on elastic wave theory, and using data that has been signal processed and error corrected as a basis for measuring gain-frequency characteristics, phase-frequency characteristics and peak sensitivity of the direct current acceleration sensor in respect of each of dynamic displacement detection function, velocity detection function and acceleration detection function of the direct current acceleration sensor.
Any one of the second, fourth and sixth mentioned methods for measuring the frequency characteristics of the direct current acceleration sensor, in which the one end surface of the metal rod is impacted with the projectile to generate the elastic wave pulse in the metal rod, further comprises taking as an input signal to the direct current acceleration sensor provided on the other end surface of the metal rod dynamic displacement, velocity or acceleration in a direction normal to the other end surface produced when the elastic wave pulse generated by the impact of the projectile reflects at the other end surface, using the direct current acceleration sensor to detect, and the optical measuring instrument to directly measure, the input signal as a function of time, carrying out signal processing with respect to an output signal from the direct current acceleration sensor and the output signal from the optical measuring instrument, and using data that has been signal processed as a basis for measuring gain-frequency characteristics, phase-frequency characteristics and peak sensitivity of the direct current acceleration sensor in respect of each of dynamic displacement detection function, velocity detection function and acceleration detection function of the direct current acceleration sensor.
Any one of the first, third and fifth mentioned methods for measuring the frequency characteristics of the direct current acceleration sensor, in which the one end surface of the metal rod is impacted with the projectile to generate the elastic wave pulse in the metal rod, further comprises taking as an input signal to the direct current acceleration sensor provided on the other end surface of the metal rod dynamic displacement, velocity or acceleration in a direction normal to the other end surface produced when the elastic wave pulse generated by the impact of the projectile reflects at the other end surface, using the direct current acceleration sensor to detect, and the strain gauge provided on the side surface of the metal rod to measure, the input signal as a function of time, carrying out signal processing of an output signal from the direct current acceleration sensor and an output signal from the strain gauge, carrying out error correction of the output signal from the strain gauge based on elastic wave theory, using a correction function relating to dynamic characteristics of the strain gauge to correct results of measurements by the gauge, and using data that has been signal processed, error corrected and measurement-result-corrected as a basis for measuring gain-frequency characteristics, phase-frequency characteristics and peak sensitivity of the direct current acceleration sensor in respect of each of dynamic displacement detection function, velocity detection function and acceleration detection function of the direct current acceleration sensor.
In any one of the seventh, eighth and tenth mentioned methods for measuring the frequency characteristics of the direct current acceleration sensor, the strain gauge provided on the side surface of the metal rod is composed of a plurality of strain gauges provided at different distances from the one end surface of the metal rod, or a plurality of strain gauges provided on a circumference of the metal rod at equal distances from the one end surface of the metal rod in any one of seventh, eighth, tenth and eleventh mentioned method.
In any one of the seventh to eleventh mentioned methods for measuring the frequency characteristics of the direct current acceleration sensor, the projectile that impacts the one end surface of the metal rod is composed of a plurality of round, concentric projectiles launched from a launch apparatus that includes multiple round, concentric launch tubes, in which the launch apparatus can precisely and independently control launch timing of each projectile launched.
The present invention further provides an apparatus for measuring frequency characteristics of a direct current acceleration sensor comprising a metal rod support apparatus that supports a metal rod with a center axis thereof aligned with a direction of gravity acceleration, a launch apparatus for impacting one of end surfaces of a metal rod with a projectile to propagate an elastic wave pulse in the metal rod, a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, a strain gauge provided on a side surface of the metal rod to measure metal rod strain caused by the impact of the projectile against the other end surface of the metal rod, and a processor for calculating a frequency response of the direct current acceleration sensor from a signal from the direct current acceleration sensor and a signal from the strain gauge.
The present invention also provides an apparatus for measuring frequency characteristics of a direct current acceleration sensor comprising a metal rod support apparatus that supports a metal rod with a center axis thereof aligned with a direction of gravity acceleration, a launch apparatus for impacting one of end surfaces of a metal rod with a projectile to propagate an elastic wave pulse in the metal rod, a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, an optical measuring instrument for measuring a velocity of motion of the other end surface of the metal rod arising when the elastic wave pulse reflects at the other end surface of the metal rod, and a processor for calculating a frequency response of the direct current acceleration sensor from a signal from the direct current acceleration sensor and a signal from the optical measuring instrument.
The present invention also provides an apparatus for measuring frequency characteristics of a direct current acceleration sensor comprising a metal rod support apparatus that supports a metal rod with a center axis thereof inclined at a prescribed angle to a direction of gravity acceleration, a launch apparatus for impacting one of end surfaces of the metal rod with a projectile to propagate an elastic wave pulse in the metal rod, a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, a strain gauge provided on a side surface of the metal rod to measure metal rod strain caused by the impact of the projectile against the other end surface of the metal rod, and a processor that obtains a frequency response of the direct current acceleration sensor, with the direct current acceleration sensor affected by the gravity acceleration, from a signal from the direct current acceleration sensor and a signal from the strain gauge and compares data of the frequency response of the direct current acceleration sensor with data of the frequency response calculated by the processor in the first mentioned apparatus to calculate characteristics with respect to the gravity acceleration in the frequency response of the direct current acceleration sensor.
The present invention also provides an apparatus for measuring frequency characteristics of a direct current acceleration sensor comprising a metal rod support apparatus that supports a metal rod with a center axis thereof inclined at a prescribed angle to a direction of gravity acceleration, a launch apparatus for impacting one of end surfaces of the metal rod with a projectile to generate and propagate an elastic wave pulse in the metal rod, a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, an optical measuring instrument for measuring a velocity of motion of the other end surface of the metal rod arising when the elastic wave pulse reflects at the other end surface of the metal rod, and a processor that obtains a frequency response of the direct current acceleration sensor, with the direct current acceleration sensor affected by the gravity acceleration, from a signal from the direct current acceleration sensor and a signal from the optical measuring instrument and compares data of the frequency response of the direct current acceleration sensor with data of the frequency response calculated by the processor in the second mentioned apparatus to calculate characteristics with respect to the gravity acceleration in the frequency response of the direct current acceleration sensor.
The present invention also provides an apparatus for measuring frequency characteristics of a direct current acceleration sensor comprising a metal rod support apparatus that supports a metal rod with a center axis thereof aligned with a direction of gravity acceleration, releases support of the metal rod to produce a free fall state and re-supports it after a prescribed time, a launch apparatus that during a period of releasing the support of the metal rod impacts one of end surfaces of the metal rod with a projectile to generate an elastic wave pulse in the metal rod, a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod, a strain gauge provided on a side surface of the metal rod to measure metal rod strain caused by the impact of the projectile against the other end surface of the metal rod, and a processor for calculating a frequency response of the direct current acceleration sensor from a signal from the direct current acceleration sensor and a signal from the strain gauge.
The present invention also provides an apparatus for measuring frequency characteristics of a direct current acceleration sensor comprising a metal rod support apparatus that supports a metal rod with a center axis thereof aligned with a direction of gravity acceleration, releases support of the metal rod to produce a free fall state and re-supports it after a prescribed time, a launch apparatus that during a period of releasing the support of the metal rod impacts one of end surfaces of the metal rod with a projectile to generate an elastic wave pulse in the metal rod, a direct current acceleration sensor provided on the other of the end surfaces of the metal rod to detect an acceleration arising when the elastic wave pulse reflects at the other end surface of the metal rod during the period of releasing the support of the metal rod, an optical measuring instrument for measuring a velocity of motion of the other end surface of the metal rod arising when the elastic wave pulse reflects at the other end surface of the metal rod, and a processor for calculating a frequency response of the direct current acceleration sensor from a signal from the direct current acceleration sensor and a signal from the optical measuring instrument.
In any one of the first, third and fifth mentioned apparatus for measuring frequency characteristics of a direct current acceleration sensor including the launch apparatus for impacting the one end surface of the metal rod with the projectile to generate the elastic wave pulse in the metal rod, the direct current acceleration sensor detects an input signal as a function of time standing for dynamic displacement, velocity or acceleration in a direction normal to the other end surface produced when the elastic wave pulse generated by the impact of the projectile reflects at the other end surface of the metal rod, which input signal constitutes an input signal to the direct current acceleration sensor provided on the other end surface, the strain gauge provided on the side surface of the metal rod measures metal rod strain caused by the impact of the projectile against the other end surface of the metal rod, and the processor carries out signal processing with respect to an output signal from the direct current acceleration sensor and an output signal from the strain gauge and uses data that has been signal processed as a basis for measuring gain-frequency characteristics, phase-frequency characteristics and peak sensitivity of the direct current acceleration sensor in respect of each of dynamic displacement detection function, velocity detection function and acceleration detection function of the direct current acceleration sensor.
In any one of the first, third and fifth mentioned apparatus for measuring frequency characteristics of a direct current acceleration sensor including the launch apparatus for impacting the one end surface of the metal rod with the projectile to generate the elastic wave pulse in the metal rod, the direct current acceleration sensor detects an input signal as a function of time standing for dynamic displacement, velocity or acceleration in a direction normal to the other end surface produced when the elastic wave pulse generated by the impact of the projectile reflects at the other end surface of the metal rod, which input signal constitutes an input signal to the direct current acceleration sensor provided on the other end surface of the metal rod, the strain gauge provided on the side surface of the metal rod measures metal rod strain caused by the impact of the projectile against the other end surface of the metal rod, and the processor carries out signal processing with respect to an output signal from the direct current acceleration sensor and an output signal from the strain gauge, carries out error correction of the output signal from the strain gauge based on elastic wave theory, and uses data that has been signal processed and error corrected as a basis for measuring gain-frequency characteristics, phase-frequency characteristics and peak sensitivity of the direct current acceleration sensor in respect of each of dynamic displacement detection function, velocity detection function and acceleration detection function of the direct current acceleration sensor.
In any one of the second, fourth and sixth mentioned apparatus for measuring frequency characteristics of a direct current acceleration sensor including the launch apparatus for impacting the one end surface of the metal rod with the projectile to generate the elastic wave pulse in the metal rod, the direct current acceleration sensor detects an input signal as a function of time standing for dynamic displacement, velocity or acceleration in a direction normal to the other end surface produced when the elastic wave pulse generated by the impact of the projectile reflects at the other end surface of the metal rod, which input signal constitutes an input signal to the direct current acceleration sensor provided on the other end surface, the optical measuring instrument directly detects the input signal, and the processor carries out signal processing with respect to an output signal from the direct current acceleration sensor and an output signal from the optical measuring instrument and uses data that has been signal processed as a basis for measuring gain-frequency characteristics, phase-frequency characteristics and peak sensitivity of the direct current acceleration sensor in respect of each of dynamic displacement detection function, velocity detection function and acceleration detection function of the direct current acceleration sensor.
In any one of the first, third and fifth mentioned apparatus for measuring frequency characteristics of a direct current acceleration sensor including the launch apparatus for impacting the one end surface of the metal rod with the projectile to generate the elastic wave pulse in the metal rod, the direct current acceleration sensor detects an input signal as a function of time standing for dynamic displacement, velocity or acceleration in a direction normal to the other end surface produced when the elastic wave pulse generated by the impact of the projectile reflects at the other end surface of the metal rod, which input signal constitutes an input signal to the direct current acceleration sensor provided on the other end surface, the strain gauge provided on the side surface of the metal rod measures metal rod strain caused by the impact of the projectile against the other end surface of the metal rod, and the processor carries out signal processing with respect to an output signal from the direct current acceleration sensor and an output signal from the strain gauge, carries out error correction of the output signal from the strain gauge based on elastic wave theory, and uses data that has been signal processed and error corrected as a basis for measuring gain-frequency characteristics, phase-frequency characteristics and peak sensitivity of the direct current acceleration sensor in respect of each of dynamic displacement detection function, velocity detection function and acceleration detection function of the direct current acceleration sensor.
In any one of the seventh, eighth and tenth mentioned apparatus for measuring frequency characteristics of a direct current acceleration sensor, the strain gauge provided on the side surface of the metal rod is composed of a plurality of strain gauges provided at different distances from the one end surface of the metal rod, or a plurality of strain gauges provided at equal distances from the one end surface of the metal rod in any one of the seventh, eighth, tenth and eleventh mentioned apparatus.
In any one of the apparatus for measuring frequency characteristics of a direct current acceleration sensor, the projectile that impacts the one end surface of the metal rod is composed of a plurality of round, concentric projectiles launched from the launch apparatus that includes multiple round, concentric launch tubes, and the launch apparatus can precisely and independently control launch timing of each projectile launched.
In any one of the apparatus for measuring frequency characteristics of a direct current acceleration sensor, the launch tube in the launch apparatus that launches the projectile has a surface treated to reduce friction with the projectile.
In any one of the apparatus for measuring frequency characteristics of a direct current acceleration sensor, the apparatus for measuring the frequency characteristics of the direct current acceleration sensor measures frequency characteristics from shock acceleration in a low peak, narrow frequency band region of the direct current acceleration sensor.
In any one of the second, fourth, sixth, ninth and fourteenth mentioned apparatus for measuring frequency characteristics of a direct current acceleration sensor, the optical measuring instrument comprises a laser interferometer.
In the twelfth mentioned apparatus for measuring frequency characteristics of an acceleration sensor, the one end surface of the metal rod contacts a metal ball and the launch apparatus that launches a plurality of projectiles in a concentric circle from the multiple launch tubes precisely controls launch timing with respect to the metal ball, to generate an elastic wave pulse in the metal rod.
In any one of the first to fifteenth mentioned apparatus for measuring frequency characteristics of an acceleration sensor, the projectile has a structure that is a lamination of different materials to control a frequency band of the elastic wave pulse generated in the metal rod by the impact of the projectile.
In any one of the first to fifteenth mentioned apparatus for measuring frequency characteristics of an acceleration sensor, in accordance with a theoretical propagation of the elastic wave in the metal rod, when obtaining transient signal distortion of an elastic wave pulse from the strain gauge output signal incident on the one end surface, at least a primary term or up to a high-order term of a series-expanded Skalak's analytic solution is used.
In any one of the apparatus for measuring frequency characteristics of an acceleration sensor, the direct current acceleration sensor has a peak sensitivity determined in accordance with an input acceleration waveform and frequency band produced by a plurality of projectiles launched from the launch apparatus with precisely controlled launch timing.
As described above, in accordance with the present invention, an elastic wave pulse is generated in a metal rod supported in alignment with a direction of gravity acceleration or at a prescribed angle thereto by impacting a projectile against one end surface of the metal rod, an acceleration sensor is used to measure the acceleration of the motion of the other end surface of the metal rod, a laser interferometer or strain gauge is used to measure the motion of the other end surface, the measurement signal is processed and corrected, and the processed result and the measured values obtained by the acceleration sensor are used to obtain the frequency response of the acceleration sensor. Therefore, the shock acceleration waveform and the frequency band can be freely controlled and the frequency characteristics of the direct current acceleration sensor that detects the direct current acceleration can be accurately and easily measured and evaluated, including evaluation of the effect of the gravity acceleration. Also, the duration time, peak value, waveform spectra and the like of the acceleration waveform imparted with respect to the direct current acceleration sensor to be calibrated can be readily controlled, enabling shock acceleration to be generated and the direct current acceleration sensor to be calibrated.